It has long been known to use engine lubrication oil to advance or retard the timing of fuel injection in a diesel engine. A timing control arrangement similar to the type contemplated for use with the present invention is shown in FIG. 1. As disclosed in U.S. Pat. No. 4,249,499 to Perr, the fuel injector shown in FIG. 1 includes a cam shaft 1 carrying cam lobes 3 and 5 for operating a rocker arm 7 via a link 9. Rotation of cam shaft 1 causes rocker arm 7 to rotate about shaft 11 to reciprocate injector plunger 13 via the link 9 and timing control tappet 15. Although normal timing is ideal for a range of engine connected operating conditions, it results in incomplete combustion during idling and low engine speeds because of insufficient pressure in the combustion chamber. Incomplete combustion results in high hydrocarbon emissions and low fuel economy, problems that can be alleviated by injecting fuel into the combustion cylinder sooner.
In the fuel injector shown in FIG. 1, advanced timing is achieved by introducing timing fluid into a timing chamber 17, thereby producing a height of fluid which lengthens the link between rocker arm 7 and injector plunger 13. As a result of this lengthened linkage, injector plunger 13 reaches its bottom-most position at an earlier point in the rotation of cam shaft 1. Accordingly, fuel injection occurs at a point in the combustion cycle when the piston of the engine is still moving upward, and while the combustion chamber size is still decreasing This advancement of injection produces combustion at higher pressures than normal timing because during normal timing injection occurs at a point close to the top dead center position of the piston, and most combustion takes place while the piston is moving downward to increase the combustion chamber size.
The specific operation of timing advancement will become more clear from a study of FIGS. 2 and 3 as compared with FIG. 1. FIG. 1 illustrates the injector parts at the end of an injection stroke wherein plunger 13 is in the down position Note that timing chamber 17 contains a metered amount of timing fluid, which has advanced the downward movement of plunger 13. FIG. 2 illustrates the timing control tappet of FIG. 1 after timing fluid has drained from chamber 17 and injector plunger 13 has retracted to a position above the point when timing fluid enters timing chamber 17. FIG. 3 illustrates the actual metering of fluid into chamber 17.
Whether and how much timing fluid will be supplied to the timing chamber 17 of the tappet is a function of the pressure of the timing fluid. When the pressure of the timing fluid supply is insufficient to overcome the closure force of check valve 18 in passageway 19, no timing fluid is admitted to chamber 17. Furthermore, the extent to which the pressure of the timing fluid supply exceeds that necessary to open the check valve 18 determines how much timing fluid will actually enter chamber 17. Thus, because timing chamber 17 can be filled during only a limited portion of the cycle of camshaft 1, if adequate supply pressure is not maintained, even if check valve 18 opens, a proper timing advance will not be obtained. However, due to temperature effects upon the viscosity of the timing fluid, especially the lubricant normally used as a timing fluid, sufficient pressure to properly fill the timing control tappets has been very difficult to achieve under all operating conditions with the prior art devices.
For example, in an embodiment of the prior art tappets, shown in FIGS. 1-3, engine lubrication oil is used as the timing fluid, cold engine lubrication oil is highly viscous. Thus, when the lubrication oil is cold, the timing chamber 17 may fill only partially during the portion of the cycle allowing flow through passageway 18, so that timing is only partially advanced. Moreover, during operation with very cold lubrication oil (i.e., in the range below 0 degrees F.), timing chamber 17 may not fill at all. In such a situation, even though advanced timing may be desired, normal timing nonetheless results. Failure to properly obtain the appropriate timing advance leads to such undesirable effects as incomplete combustion, poor idling characteristics, low fuel economy, and the emission of white smoke which is high in hydrocarbons.
As illustrated by the solid line in FIGS. 4 and 5, even though the oil pressure at engine block drillings of the lubrication system is maintained constant (FIG. 5), the oil pressure at the tappets in prior art devices does not reach the necessary pressure level, indicated by the broken line in FIG. 4, until the engine warms up and oil viscosity, drops Therefore, until a temperature corresponding to point A in FIG. 4 is reached, the advanced timing function is not properly performed due to the pressure drop caused by the cumulative boundary layer effects resulting from pumping very thick oil through relatively narrow passageways.
Devices for measuring oil viscosity are known as disclosed in U.S. Pat. No. 1,863,090 to Albersheim et al and U.S. Pat. No. 2,050,242 to Booth. Neither of these devices, however, effects a change in the pressure of oil responsive to its viscosity. Although Booth recognizes that more pressure is required for the flow of more viscous oil, neither patent discloses means for increasing oil pressure to critical engine parts when viscosity increases are observed.
U.S. Pat. No. 2,194,605 to Mapel and U.S. Pat. No. 2,035,951 to Eckstein disclose other apparatus for measuring oil viscosity. Mapel recognizes that a greater pressure must be used to effect the same rate of flow for thick oil, but uses this relationship only as an indication of viscosity. Mapel does not change oil pressure in response to high viscosity oil.
U.S. Pat. No. 3,938,369 to de Bok discloses an invention which heats a fluid until a desired viscosity is achieved Although de Bok establish desirable flow characteristics upon sensing an undesirable viscosity level, the de Bok device requires a heater for heating the fluid until a desired viscosity is obtained which would be otherwise unnecessary, and thereby would increase the costs of manufacturing and maintaining an engine. Furthermore, although a heater may provide sufficient heat to achieve the proper viscosity of small amounts of fuel, as is de Bok's purpose, such a heater would be incapable of heating the quantity of oil required for lubrication in a diesel engine in a fast enough time to provide the degree of responsiveness that would be required to be useful for achieving proper operation of variable timing tappets.
U.S. Pat. No. 2,051,026 to Booth discloses an engine lubricating system designed to supply lubricating oil to the engine bearings at uniform viscosity in which only a small amount of oil from a hot oil sump is circulated through the engine when the engine is started, and as viscosity drops, oil is also admitted to the lubrication system from a larger, cold oil sump in a manner designed to hold the oil at a temperature which will yield the correct oil viscosity. Although this arrangement provides an almost immediate supply of oil of a desired viscosity to the bearings, the arrangement is disadvantageous because it requires two oil sumps (one hot and one cold) and associated controls, sensors, and piping for mixing hot and cold oil to achieve the desired viscosity. Furthermore, such a necessarily small hot oil sump is not designed to meet the needs of a tappet system of the type initially mentioned.
In short, no apparatus is known which not only senses the viscosity of lubricating oil, but also adjust the output pressure from a lubrication oil pump in response thereto. Particularly, there is no apparatus known that increases the pressure of oil delivered to timing control tappets upon sensing that the oil viscosity is above a predetermined level to ensure proper operation of the timing control tappets.